Improving patient waiting time of centralized front office service in a regional hub hospital using the discrete event simulation model.

BACKGROUND: Today, hospital rankings are based not only on basic clinical indicators, but even on quality service indicators such as patient waiting times. Improving these indicators is a very important issue for hospital management, so finding a solution to achieve it in a simple and effective way is one of the greatest goals. OBJECTIVES: The aim of this article is to evaluate the use of a discrete event simulation model to improve healthcare processes and reduce waiting time of patients and hospital costs. METHODS: The case study proposed in this paper is the reorganization of non-clinical front office operation for the patients (i.e. booking of exams, delivering medical reports, etc.) of the Careggi University Hospital of Florence, to optimize the utilization of the human resources and to improve performances of the process. RESULTS: The development and validation of the model was made according to an analysis of real processes and data, pre and post implementation of model outcomes. The new organization shows a decrease of waiting times from an average value of 10 minutes and 37 seconds to 5 minutes and 57 seconds (-44%). CONCLUSIONS: This paper shows that discrete event simulation could be a precise, cost-limited tool to optimize hospital processes and performance.

Role of AMP-activated protein kinase activators in antiproliferative multi-drug pituitary tumour therapies: effects of combined treatments with compounds affecting the mTOR-p70S6 kinase axis in cultured pituitary tumour cells.

AMP-activated protein kinase (AMPK) is activated under conditions that deplete cellular ATP levels and elevate AMP levels. We have recently shown that AMPK can represent a valid target for improving the medical treatment of growth hormone (GH)-secreting pituitary adenomas and the effects of its activation or inhibition in pituitary tumour cells are worthy of further characterisation. We aimed to determine whether AMPK may have a role in combined antiproliferative therapies based on multiple drugs targeting cell anabolic functions at different levels in pituitary tumour cells to overcome the risk of cell growth escape phenomena. Accordingly, we tried to determine whether a rationale exists in combining compounds activating AMPK with compounds targeting the phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR/p70S6K signalling pathway. AMPK down-regulation by specific small-interfering RNAs confirmed that activated AMPK had a role in restraining growth of GH3 cells. Hence, we compared the effects of compounds directly targeting the mTOR-p70S6K axis, namely the mTOR inhibitor rapamycin and the p70S6K inhibitor PF-4708671, with the effects of the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) on cell signalling and cell growth, in rat pituitary GH3 cells. AICAR was able to reduce growth factor-induced p70S6K activity, as shown by the decrease of phospho-p70S6K levels. However, it was far less effective than rapamycin and PF-4708671. We observed significant differences between the growth inhibitory effects of the three compounds in GH3 and GH1 cells. Interestingly, PF-4708671 was devoid of any effect. AICAR was at least as effective as rapamycin and the co-treatment was more effective than single treatments. AICAR induced apoptosis of GH3 cells, whereas rapamycin caused preferentially a decrease of cell proliferation. Finally, AICAR and rapamycin differed in their actions on growth factor-induced extracellular signal regulated kinase 1/2 phosphorylation. In conclusion, the results of the present study suggest the increased efficacy of combined antiproliferative therapies, including rapamycin analogues and AMPK activators in GH-secreting pituitary tumours, as a result of complementary and only partially overlapping mechanisms of action.

New understanding and treatments for osteoporosis.

To summarize promising areas of investigation in osteoporosis and to stimulate further research in this area, as discussed in a recent international conference. Over the recent years, there has been an improvement in the knowledge of molecular pathways involved in bone formation and resorption with the development of new drugs to treat osteoporosis. Intact parathyroid hormone, teriparatide, and anti-sclerostin monoclonal antibody are anabolic drugs, whereas denosumab and odanacatib are anti-resorptive drugs with more reversible effects as compared to bisphosphonates. Anabolic and anti-resorptive agents have different effects on bone, and research in this area includes the efficacy of combination and sequential therapies with them. New insights in the molecular pathways of bone remodeling have clarified the mechanisms responsible for skeletal fragility in several forms of secondary osteoporosis, such as that occurring in type 2 diabetes, following drug exposure and systemic inflammatory diseases. Future research is needed to address the efficacy of anti-osteoporotic drugs in these more recently recognized conditions of skeletal fragility. Osteoporosis continues to be an important field of biomedical research.

Invited review: Dairy intake and bone health: a viewpoint from the state of the art.

The aim of this review was to focus on the complex relationships between milk and dairy products intake and bone health, with particular emphasis on osteoporosis. The literature was extensively examined to provide an objective overview of the most significant achievements on the subject. Osteoporosis can be defined as a disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk. Although the major determinants of peak bone mass and strength are genetic, major factors during childhood and adolescence may affect the ability to achieve peak bone mass. These include nutrition, particularly calcium and protein intake, physical activity, endocrine status, as well as exposure to a wide variety of risk factors. The role of calcium intake in determining bone mineral mass is well recognized to be the most critical nutritional factor to achieve optimal peak bone mass. The greatest amount of dietary calcium is obtained from milk and dairy foods, which also provide the human diet with vitamin D (particularly for products fortified with vitamin D), potassium, and other macro- and micronutrients. Although studies supporting the beneficial effects of milk or calcium on bone health are predominant in the literature, perplexity or discordance on this subject was expressed by some authors. Discordant data, mainly on the risk of fractures, provided limited proof of the unfavorable effect of dairy intake. More often, discordant works indicate no effect of dairy consumption on bone safety. Some considerations can be drawn from this viewpoint. Milk and dairy products are an optimal source of calcium as well as of other limiting nutrients (e.g., potassium and magnesium), with important effects on bone health. Bioactive components occurring in milk and dairy products may play an essential role on bone metabolism, as shown by in vivo and in vitro studies on colostrum acidic proteins and milk basic proteins. Calcium intake positively affects bone mass and is crucial in childhood and youth for correct bone development. In elderly people, calcium intake as well as vitamin D availability should be carefully checked. As a general conclusion, calcium is essential for bone health, although it will not prevent bone loss due to other factors; in this context, milk and dairy foods are bioavailable, relatively inexpensive sources of calcium for the human diet.

Feeding behavior during long-term hexarelin administration in young and old rats.

Ghrelin, a 28-amino-acid peptide isolated from the stomach, is the natural ligand of the GH-secretagogues receptor-1a (GHS-R1a) and, so far, the only discovered circulating appetite-stimulating hormone. Similarly to ghrelin, many synthetic compounds belonging to the GHS family stimulate both GH secretion and feeding, whereas some stimulate GH secretion only. In the past years, studies have focused on the potential of the GHS to stimulate GH release during long-term treatment in humans and experimental animals. Few data are available about the extraendocrine effects of the GHS during several weeks of treatment, particularly in old rats. The aim of the present study was first to identify the lowest dose of hexarelin giving maximal stimulation of food intake both in young (3-month-old) and old rats (24-month-old). A dose-response study (80-320 microg/kg, s.c.) revealed that hexarelin at the dose of 80 microg/kg gave reproducibly maximal stimulation of food consumption in young as well as in old rats. Second, we evaluated the effect of 8-week daily sc treatment with hexarelin in young and old male rats. The outcome of the chronic study was that hexarelin (80 microg/kg, s.c., once daily) maintained a persistent significant orexigenic action throughout the treatment period, both in young and old rats. Interestingly, hexarelin treatment did not affect body weight gain either in young or old rats. We conclude that hexarelin is endowed with long-lasting orexigenic activity and might represent a potential therapeutic approach for pathological conditions characterized by a decline in food intake.

GH-releasing peptides and bone.

It has been extensively demonstrated that GH secretagogues (GHS) play a role in the regulation of bone metabolism in animals and humans. Unlike GH, administration of GHS does not increase bone resorption markers, suggesting that a mechanism exclusively linked to GH release cannot account for the effect of these compounds. On this line, we investigated the effect of GHS and ghrelin, the endogenous ligand of GHS receptors, on bone cells. We found that both hexarelin and ghrelin significantly stimulated cell proliferation and increased alkaline phosphatase and osteocalcin production in primary cultures of rat calvaria osteoblasts. In the same cells, we were able to detect the mRNA for the GHS receptor by RT-PCR and the corresponding protein by Western blot, indicating that ghrelin and GHS may bind and activate this receptor. Two isoforms of GHS receptors (GHS-R), which are presumably the result of alternate processing of pre-mRNA, have been identified and designed receptors 1a (R1a) and 1b (R1b). Ghrelin, the endogenous ligand of the GHS receptors, binds with high affinity GHS-R1a only. Unlike fetal calvaria cells, osteoblasts derived from adult rat tibia did not express the GHS-R1 a, but only the biologically inactive isoform GHS-R1b. The latter isoform was present in only one of the three specimens of human osteoblasts obtained from the iliac crest or the upper femur of patients during surgery. These results would indicate that only osteoblasts from fetal bone express functional receptors responsive to ghrelin and GHS.

Effects of hypothyroidism and endocrine disruptor-dependent non-thyroidal illness syndrome on the GnRH-gonadotroph axis of the adult male rat.

Effects of primary hypothyroidism (HYPO) on the male gonadal axis are controversial, with only scanty data on the gonadotroph cell response and no information on GnRH tuberoinfundibular neurons, even in animal models. HYPO has been reported to variably induce hypogonadotropic hypogonadism, a hypergonadotropic state, or to have no effects on basal levels of pituitary gonadotropins, both in adult male rats and humans. Similarly, the exogenous administration of GnRH to HYPO rats and humans may increase or decrease gonadotropin secretion. Since inhibitory effects of HYPO on the GnRH-gonadotropin axis are reversed by replacement with L-T4, it has been suggested that thyroid hormone (TH) may regulate tuberoinfundibular GnRH and pituitary gonadotropin biosynthesis and/or secretion. To shed light on this hypothesis, we conducted immunocytochemical studies on the distribution and immunostaining characteristics of hypophysiotropic GnRH neurons, LH, PRL and vasoactive intestinal polypeptide (VIP) immunoreactive (IR) cells in the pituitary of adult, male rats. We show that HYPO reduces IR-GnRH in a restricted population of tuberoinfundibular perikarya and their proximal axons compared to euthyroid controls, but increases IR-VIP both in pituitary cells in direct association with LH-gonadotrophs and within IR-LH cells, itself. We propose that VIP may serve as a juxtacrine/paracrine/autocrine regulator of LH secretion and that, when GnRH biosynthesis is reduced by HYPO, gonadotropin secretion may be rescued by local activating effects of VIP. Polychlorinated biphenyls (PCB), industry toxicants found in food and water, also have inhibitory effects on the gonadal axis, decreasing fertility and suppressing basal and GnRHinduced LH release in male rats. Since PCB may also exert endocrine disruptor-dependent (EDD) effects on the thyroid axis producing a non-thyroidal illness syndrome (NTIS) (coined EDD-NTIS), we developed a rat model of EDD-NTIS to determine whether central hypothyroidism may contribute to the pathophysiology of PCB-induced hypogonadism. On the basis of preliminary animal data, we speculate that one of the mechanisms for Partial Androgen Deficiency of the Aging Male may involve central hypothyroidism and EDD-NTIS, resulting in inhibition of the GnRH-gonadotroph axis.

Characterization of the resistance to the anorectic and endocrine effects of leptin in obesity-prone and obesity-resistant rats fed a high-fat diet.

Leptin produced by adipocytes controls body weight by restraining food intake and enhancing energy expenditure at the hypothalamic level. The diet-induced increase in fat mass is associated with the presence of elevated circulating leptin levels, suggesting the development of resistance to its anorectic effect. Rats, like humans, show different susceptibility to diet-induced obesity. The aim of the present study was to compare the degree of leptin resistance in obesity-prone (OP) vs obesity-resistant (OR) rats on a moderate high-fat (HF) diet and to establish if the effects of leptin on hypothalamo-pituitary endocrine functions were preserved. Starting from 6 weeks after birth, male Sprague-Dawley rats were fed on either a commercial HF diet (fat content: 20% of total calorie intake) or a standard pellet chow (CONT diet, fat content: 3%). After 12 weeks of diet, rats fed on HF diet were significantly heavier than rats fed on CONT diet. Animals fed on HF diet were ranked according to body weight; the two tails of the distribution were called OP and OR rats respectively. A polyethylene cannula was implanted into the right ventricle of rats 1 week before central leptin administration. After 12 weeks of HF feeding, both OR and OP rats were resistant to central leptin administration (10 mug, i.c.v.) (24 h calorie intake as a percent of vehicle-treated rats: CONT rats, 62 [50; 78]; OR, 93 [66; 118]; OP, 90 [70; 120] as medians and 95% confidence intervals (CIs) of six rats for each group). Conversely, after 32 weeks of diet both OR and OP rats were partially responsive to 10 mug leptin i.c.v. as compared with CONT rats (24 h calorie intake as a percent of vehicle-treated rats: CONT rats, 60 [50; 67]; OR, 65 [50; 80]; OP, 80 [60; 98] as medians and 95% CIs of six rats for each group); the decrease of food intake following 200 mug leptin i.p. administration was similar in all the three groups (calorie intake as a percent of vehicle-treated rats: 86 [80; 92] as median and 95% CI). The long-term intake of HF diet caused hyperleptinemia, hyperinsulinemia and higher plasma glucose levels in OP rats as compared with CONT rats. Plasma thyroxine (T4) was lower in all the rats fed the HF diet as compared with CONT. i.c.v. administration of leptin after 32 weeks of diet restored normal insulin levels in OP rats. Moreover, leptin increased plasma T4 concentration and strongly enhanced GH mRNA expression in the pituitary of OP as well as OR rats (180+/-10% vs vehicle-treated rats). In conclusion, long-term intake of HF diet induced a partial central resistance to the anorectic effect of leptin in both lean and fat animals; the neuroendocrine effects of leptin on T4 and GH were preserved.

Serum osteoprotegerin and receptor activator of nuclear factors kB (RANKL) concentrations in normal children and in children with pubertal precocity, Turner's syndrome and rheumatoid arthritis.

BACKGROUND: Osteoprotegerin (OPG) is a secreted member of the TNF receptor superfamily. OPG is made by osteoblastic cells and is expressed in a wide variety of cell and tissue types. It acts as a decoy receptor by binding the receptor activator of nuclear factors kB (RANKL) and preventing RANKL-induced osteoclast formation and differentiation. Numerous cytokines and hormones (TGF-beta, PTH, vitamin D, glucocorticoids and oestrogens) exert their effects on osteoclastogenesis by regulating the production of OPG. PATIENTS AND METHODS: In the present study we compared serum OPG and RANKL concentrations in a group of normal children (1-14 years old) with those of pair-aged children affected by different diseases [Turner's syndrome (TS), early/precocious puberty (PP) and rheumatoid arthritis (RA)]. OPG and RANKL concentrations were measured by an enzyme immunoassay method using a commercial kit. RESULTS: Mean (+/- SD) OPG level in normal children was 4.05 +/- 1.63 pmol/l with no difference between males and females. OPG values in children 1-4 years old (5.87 +/- 2.22 pmol/l) were significantly higher than in children 4-14 years old (3.55 +/- 0.97 pmol/l). OPG levels in children with RA were significantly higher than in controls (6.33 +/- 2.57 pmol/l vs. 4.05 +/- 1.63 pmol/l, P < 0.01); patients with TS or PP had OPG levels superimposable to those of controls (2.61 +/- 0.67 pmol/l and 3.99 +/- 0.85 pmol/l, respectively), but in TS OPG levels were significantly lower than in age-matched females. Mean RANKL concentration in normal subjects was 0.81 +/- 1.55 pmol/l; there was a slight decline in RANKL levels with age. RANKL concentrations in subjects with TS, PP, RA and controls did not differ significantly, and did not differ from those published in adult normal subjects. CONCLUSIONS: It appears from our data that OPG serum levels in healthy children aged > 4 years are similar to those present in young adult men, with higher levels in the first 4 years of life. Although the meaning of the alterations of OPG levels observed in pathological conditions is still obscure, they appear potentially interesting in view of a key role played by this protein in bone homeostasis.

PLGA microspheres for oral osteopenia treatment: preliminary "in vitro"/"in vivo" evaluation.

The aim of this work was to prepare and to evaluate "in vitro"/"in vivo" microspheres based on poly(D,L-lactide-co-glycolide) copolymers containing ipriflavone, for the local treatment of oral bone loss. The first objective was the preparation and "in vitro" characterization of ipriflavone loaded microspheres, by emulsion/solvent evaporation method. Process parameters such as drug:polymer weight ratio, and molecular weight of copolymers, were also investigated. The second objective was to elaborate a suitable animal model of mandibular osteoporosis, to evaluate the efficacy of these microparticulate drug delivery systems. "In vivo" experiments were carried out on female rats, in which oral osteopenia was induced by gonadectomy and molar avulsion. Morphometric analysis of mandibular segment were carried out to quantify the development of oral osteopenia and the efficacy of drug loaded microspheres. Results showed that ipriflavone loaded PLGA microspheres can be successfully obtained with good "in vitro" characteristics, utilizing the emulsification/solvent evaporation method. "In vivo" experiments revealed that local administration of microspheres produced only mild inflammation on the injection site. Morphometric analyses showed, at the level of the third molar, a slight increase in spongy and total bone mass on rat jaw treated with microspheres with respect to control. Control animals exhibited a scarce degree of osteopenia demonstrating that this animal model is not suitable for this purpose.

Bone effects of hexarelin, a GH-releasing peptide, in female rats: influence of estrogen milieu.

OBJECTIVE: The present study was performed to evaluate the potential influence of the estrogen milieu in modulating the effects of GH/IGF stimulation by a GH-releasing peptide, hexarelin (HEXA), on bone metabolism and mineral density in middle-aged female rats. METHODS: HEXA was administered for 60 days (50 microg/kg s.c. twice a day) to intact and ovariectomized (OVX) 11-month-old female rats and changes in bone parameters were evaluated with respect to those of the same rats under baseline conditions and with those of control rats (intact and OVX) administered isovolumetric amounts of physiological saline. Serum total alkaline phosphatase (ALP) and urinary deoxypyridinoline (Dpd) were measured before and at various times during HEXA treatment. Bone mineral content (BMC) and density of lumbar vertebrae and femoral mid-diaphyses were measured by dual energy X-ray absorptiometry before and after treatment. In all groups, serum IGF-I levels were determined before and during treatment and the GH secretory response to HEXA was assessed at the end of the experiment. RESULTS: In intact rats, HEXA did not modify Dpd urinary excretion, induced a trend toward an increase of serum ALP activity and significantly increased BMC (+6.5%) and bone area (+4.1%) only at lumbar vertebrae. In OVX rats, HEXA did not modify the OVX-induced increase in bone turnover markers (Dpd and ALP) and did not affect the OVX-induced vertebral bone loss, but significantly increased BMC (+7.2%) and bone area (+5.3%) at femoral mid-diaphyses. HEXA significantly increased serum IGF-I levels at day 14, but not at day 60, in both intact and OVX rats, whereas the GH secretory response to HEXA was higher in the former than in the latter. CONCLUSIONS: Overall, the present data demonstrate that chronic HEXA treatment increases BMC and bone area at lumbar vertebrae in intact rats and at femoral diaphyses in OVX rats. The different sensitivity to HEXA of the skeletal districts examined is related to the estrogen milieu and may reflect a complex interplay between estrogens and GH/IGF function.

Characterization of new selective somatostatin receptor subtype-2 (sst2) antagonists, BIM-23627 and BIM-23454. Effects of BIM-23627 on GH release in anesthetized male rats after short-term high-dose dexamethasone treatment.

We here report a pharmacological characterization of two new somatostatin (SS) receptor subtype-2 (sst2) selective antagonists by evaluating their GH-releasing activity when administered, by different routes, in anesthetized adult rats and in freely moving 10-d-old rats. Moreover, we describe the effect of these SS antagonists on the GH response to GHRH after short-term high-dose dexamethasone (DEX) treatment in young male rats. BIM-23454 and BIM-23627, given iv, were able to counteract the SS-induced inhibition of GH secretion occurring after urethane anesthesia in a dose-dependent manner. In DEX-treated animals, the GH response to GHRH was partially blunted (5-min peak values, 270 +/- 50 ng/ml in saline-treated vs. 160 +/- 10 ng/ml in DEX-treated, P < 0.05); however, the simultaneous administration of BIM-23627 (0.2 mg/kg, iv) restored higher amplitude GH pulse, leading to a significantly higher overall mean GH response (area under the curve, 4200 +/- 120 ng/ml/30 min vs. 2800 +/- 100 ng/ml/30 min after GHRH alone; P < 0.05). The SS antagonists showed a reduced GH-releasing effect when administered sc or ip, likely attributable to decreased bioavailability, as compared with the iv route. SS antagonist administration also increased plasma glucagon, insulin, and glucose levels. Based on prior reports that sst2 tonically suppresses glucagon secretion, the antagonist most likely increased glucagon secretion from the pancreatic alpha-cells, with resultant increases in plasma glucose and then insulin.

Phagocytosis and killing of Candida albicans of polymorphonuclear cells in patients with organ transplant of periodontal disease.

BACKGROUND: The easiest defence system carried out by the organism, the inflammatory response, happens with the support of phagocyting cells: the polymorphonuclear leukocytes (PMNL) or neutrophils are the most important cell line acting as the first defence of the organism against bacterial agents. Previous studies have shown a correlation between a reduction of the immune function and development of periodontal disease. Furthermore, it is well known that transplant patients show a variety of oral lesions as a consequence of their therapy, in particular to immunosuppressive drugs. The aim of this study is to evaluate the phagocytosis and killing functions of PMNL in transplant patients and in patients with periodontal disease in comparison with a group of healthy subjects. METHODS: PMNL, were isolated by spontaneous sedimentation from heparinized blood and centrifugation of plasma on density medium. Phagocytosis rate was expressed as the percentage of Candida albicans phagocyted after 20' incubation and phagocyting PMNLs. Intracellular killing was expressed as the percentage of yeast cells killed. RESULTS: We did not find a significant decrease of phagocytosis in transplant patients and patients with periodontal disease while these two groups of patients showed a decrease of PMNL killing activity in respect to healthy controls, an effect which was unrelated to the severity of periodontal disease. CONCLUSIONS: These results suggest that a reduction of killing activity, either spontaneous or drug-induced, would contribute to the development of periodontal disease.

Endocrine, metabolic and cardioprotective effects of hexarelin in obese Zucker rats.

Genetically obese male Zucker rats have an impaired secretion of GH, coupled to hyperinsulinemia, hyperlipidemia and glucose intolerance. The aim of this study was to evaluate whether a chronic treatment with hexarelin, a synthetic enkephalin-derived hexapeptide with a potent GH-releasing activity, might be able to ameliorate the somatotropic function and reverse some metabolic alterations associated with obesity in male obese Zucker rats. Furthermore, as decreased GH secretion and insulin resistance are associated with increased cardiovascular risk, we also tested the capacity of hexarelin to prevent postischemic ventricular dysfunction in hearts of male obese Zucker rats. Obese and lean male rats of the Zucker strain were treated with hexarelin (80 microgram/kg, b.i.d., s.c.) or saline (1 ml/kg, b.i.d., s.c.) for 30 days. An acute hexarelin injection (80 microgram, s.c.) at the 28th day of treatment elicited a rise in plasma GH levels in ! lean but not in obese rats (pretreated or not with hexarelin); lean rats chronically treated with hexarelin showed a greater increase in plasma GH as compared with control counterparts. At the end of the experiment, pituitary GH mRNA levels were significantly reduced in obese rats and hexarelin administration failed to increase pituitary GH mRNA and IGF-I concentrations in plasma and heart. Chronic treatment with hexarelin increased insulinemia and blood glucose levels in obese but not in lean rats, left unaltered the high triglyceride levels but significantly decreased plasma cholesterol concentrations in obese rats. Heart preparations from lean and obese Zucker rats treated with saline, subjected to low flow ischemia and reperfusion, showed at reperfusion: a) a low recovery of postischemic left ventricular developed pressure (LVDP), coupled to a substantial increase in coronary perfusion pressure, and b) a marked increase in creatine kinase released in the perfusates. Hexare! lin administration for 30 days counteracted the heart ischemic damage both in lean and obese Zucker rats. In fact, the recovery of LVDP at reperfusion was significantly higher than in controls and the increase in coronary resistance was minimal. Collectively, these data indicate that a 30-day treatment with hexarelin was unable to improve somatotropic function in male obese Zucker rats but was successful in decreasing plasma cholesterol concentrations. Hexarelin exerted a cardioprotective effect in both lean and obese rats. The heart-protective activity afforded by the peptide was divorced from any stimulation of the GH axis and is probably exerted through activation of specific cardiac receptors.

The influence of sex and gonadectomy on the growth hormone and corticosterone response to hexarelin in the rat.

The present study is designed to investigate the role of sex and gonadal status in the growth hormone (GH) and corticosterone response to hexarelin (HEXA), a GH-releasing peptide, which also causes a stimulatory action on the hypothalamic-pituitary-adrenal (HPA) axis. HEXA (80 microg/Kg) was administered intracarotid to anesthetized intact or gonadectomized male (ORC) and female (OVX) middle-aged rats. The GH stimulatory response to HEXA was gender-related since the GH increase was significantly (p < 0.001) higher in intact males (area under the curve, AUC= 12560 +/- 1784 ng/ml.45 min) than in females (AUC= 4628 +/- 257 ng/ml.45 min). This sex difference does not depend on circulating gonadal steroids since it persists in ORC (AUC = 11980 +/- 1136 ng/ml.45 min) and OVX (AUC = 5539 +/- 614 ng/ml.45 min) rats. The different effects of HEXA on corticosterone secretion detected in male and female rats are probably dependent on the prevailing activity of the HPA axis. In fact, in male rats that have low basal corticosterone levels, HEXA caused an increase in corticosterone secretion, which was significantly (p< 0.05) higher in ORC than in intact rats. The increase in corticosterone secretion by HEXA both in intact and OVX females was delayed, probably due to the elevated initial corticosterone levels, which could have activated the glucocorticoid negative feedback. We suggest that gender-specific patterns in the regulation of the hypothalamus-pituitary function could be responsible for the GH and corticosterone sexually differentiated responses to HEXA.

Hexarelin, a growth hormone - releasing peptide, counteracts bone loss in gonadectomized male rats.

The age-related decline in growth hormone (GH) secretion has been implicated in the pathogenesis of involutional bone loss. Whether restoration of GH secretion might be helpful in maintaining and/or improving bone mass during aging is still unsettled. The aim of the present study was to examine the effects of 30-day treatment with hexarelin (HEXA, 50 microg/kg subcutaneously b.i.d.), a highly effective GH-releasing compound, on bone metabolism and bone mineral density (BMD) in intact and osteopenic gonadectomized (GDX) mature male rats. Serum total alkaline phosphatase (ALP, bone formation marker) and bone resorption markers (lysylpyridinoline, LP and hydroxylysylpyridinoline, HP) were measured before and 7, 14 and 30 days after treatment. BMD was measured by dual-energy X-ray absorptiometry at lumbar vertebrae, femoral metaphysis and diaphysis before and at the end of the experiment. In intact rats, HEXA significantly (P<0.05) decreased LP (-36.3%) and HP (-22.8%) excretion at day 7, whereas it did not change serum ALP activity and BMDs. In GDX rats, HEXA completely prevented the significant (P<0. 01) increase in urinary excretion of both LP (+143.8%) and HP (+119. 4%), the early decrease in ALP activity (-26.5%) and the significant (P<0.05) decrease in BMDs in the femoral metaphysis (-7.9%) and lumbar vertebrae (-6.8%) caused by androgen deficiency. The bone-protective effects of HEXA could be attributed, at least in part, to its GH-releasing activity since chronic-treated rats maintained the GH response to an acute challenge with HEXA. The evidence that HEXA, unlike GH, inhibits bone resorption indicates that other mechanisms contribute to the bone sparing effect of HEXA.

Leptin regulates GH secretion in the rat by acting on GHRH and somatostatinergic functions.

Leptin is a hormonal product of adipose tissue whose expression reflects the body state of nutritional reserves. Previous experiments have demonstrated that leptin is one of the metabolic signals capable of regulating GH secretion. The aim of the present study was to evaluate whether CNS-mediated mechanisms underlie the GH-releasing activity of leptin. Freely moving mature male rats were injected i.c.v with leptin or isovolumetric amounts of diluent once daily for 3 days and were killed 2 h after the last administration. Central injection of leptin increased pituitary GH mRNA levels by 53. 2% and hypothalamic GHRH mRNA by 61.8%, and reduced somatostatin mRNA levels by 41.5%. To evaluate the direct effect of leptin on the pituitary, it was added alone or in combination with GHRH to primary cultures of anterior pituitary cells. Addition of leptin (10(-11)-10(-7) M) did not alter basal GH release nor the GH-releasing activity of GHRH. These results demonstrate that leptin is a metabolic signal that regulates GH secretion in the rat by acting on hypothalamic GH-regulatory hormones.

Induction and pharmacological treatment of oral osteopenia in rats.

BACKGROUND: Osteoporosis is a major public health problem, responsible for a great number of fractures, associated with devastating costs to society. In addition, oral bone loss has an enormous impact on the health quality of life of patients, affecting up to 90% of elderly individuals. The aim of this work was to elaborate an animal model of mandibular and maxillary osteoporosis in which to evaluate bone loss and possible prevention by pharmacological treatment. METHODS: Six Sprague-Dawley rats were gonadectomized and treated with clodronate (male) or 17 beta-estradiol (female) for two months. Six gonadectomized and six sham-operated rats of both sexes were treated with placebo. The mandible and maxilla, fixed and methacrylate embedded, were serially sectioned, microradiographed and processed for histomorphometric analysis. RESULTS: Gonadectomy did not modify the amount of compact and trabecular bone in mandibles of rats of either sex, treated or not with clodronate or estrogens, compared to sham-operated rats. Compared to sham-operated rats, a 10-25% increase of bone porosity was found in the maxilla of ovariectomized rats, either receiving estrogens or not, while in male rats no difference among groups could be evidenced. CONCLUSIONS: The conclusion is drawn that rats, due to their peculiar masticatory habits yielding huge loads on oral bones, do not represent a suitable experimental model for studying oral bone loss related to skeletal osteoporosis. In order to worsen oral osteopenia it would be mandatory to combine gonadectomy with a mechanical unloading (i.e. after molar extraction) of mandibular or maxillary bone.

Neuroendocrine control of growth hormone secretion.

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Higher content of insulin-like growth factor-I in dystrophic mdx mouse: potential role in the spontaneous regeneration through an electrophysiological investigation of muscle function.

Insulin-like growth factor-I (IGF-I) is known to promote proliferation and differentiation of muscle cells during growth and regeneration. Both these conditions are characterized by acquisition of specialized muscle functions, such as a large macroscopic chloride conductance (GCl), a parameter that is a target of growth hormone (GH)/IGF-I axis action on skeletal muscle. The present study has been aimed at evaluating the role of IGF-I in the spontaneous regeneration occurring in hind limb muscle of dystrophic mdx mouse. IGF-I levels have been measured in hind limb muscles, plasma and liver of mdx and control mice of 8-10 weeks and 5 months of age by radioimmunoassay. In parallel the biophysical and pharmacological properties of muscle chloride channels of extensor digitorum longus (EDL) muscle fibers of mice belonging to the same age-group have been measured electrophysiologically in vitro. At 8-10 weeks of age, significantly greater amounts of IGF-I were found in plasma and hind limb muscles of mdx mice with respect to controls. Such a difference was only just detectable and no longer statistically significant at 5 months of age. No differences were found in hepatic IGF-I levels at either age. The EDL muscle fibers of mdx mice at 8-10 weeks of age were characterized by higher GCl values and by a different pharmacological sensitivity to the enantiomers of 2-(p-chlorophenoxy)-propionic acid (CPP), specific chloride channel ligands, with respect to age-matched controls. However, these differences were no longer detected at 5 months of age. Our results suggest a role of IGF-I in the high regenerative potential of muscles from mdx mice and support the hypothesis that the biophysical and pharmacological properties of chloride channels of EDL muscle fibers are sensitive indices of the action of regeneration-promoting factors on muscle function.